The specific aims of this research are to: (1) determine whether specialized pulse characteristics of an input waveform are required to produce electromagnetic stimulation (EMS) that is effective in eliciting new bone by comparing rectangular and sinusoidal waveforms at the same pulse and burst frequencies and peak magnetic field amplitudes; (2) evaluate the biological response elicited with direct current stimulation (DCS), EMS by rectangular waveform, and EMS by sinusoidal waveform by histomorphometry; (3) determine whether chemical alterations in bone tissue, known to occur with DCS, also occur with EMS by rectangular and sinusoidal waveforms by measuring the oxygen tension, pH, and calcium ion concentration at the site of electrical treatment; (4) determine whether thermal alterations in bone tissue occur with DCS and EMS by both rectangular and sinusoidal waveforms by measuring temperature at the site of electrical treatment; and (5) examine whether the chemical or thermal alterations, if found, correlate with any of the quantitative parameters describing the biological response. Achieving the above specific aims will help to design future studies as part of an overall research program. The primary, long term objective of this program is to identify an effective technique to be used in evaluating the appropriateness of electrical stimulation for treatment of patients with loose endoprosthetic devices, osteopenic disorders, nonunions, pseudarthroses, and fractures with a high incidence for nonunion. One secondary objective is to determine the effects of electrical stimulation on nonosseous tissues that are known to be influenced by electrical stimuli. The tibial medullary canal will be the site selected to study the effects of electrical treatment. Trauma and irritation will be surgically introduced into this site as a means of obtaining cells responsive to electrical stimulation. Three groups will be treated unilaterally with either DCS, EMS by rectangular waveform, or EMS by sinusoidal waveform. One additional group will be treated without electrical stimulation to serve as separate controls. Intramedullary oxygen tension, pH, calcium ion concentration, and temperature measurements will be performed biolaterally on treatment day 0, 7, 14, and 21 using needle microelectrodes plus a transcortical, silicone rubber implant. Parameters describing the biological response will be quantitated using a morphologic data acquisition system for geometric measurements and point or feature counts from a microscopically produced video image.